In recent years, the cost for manufacturing a steel can has been reduced to expand the demand for the Steel cans as a can steel plate. For reducing the cost for manufacturing a steel can, the cost of a steel plate to be used may be reduced. Thus, as well as a two-piece can in which a drawing process is performed in a can manufacturing process, in a body or a cover of a three-piece can in which simple cylindrical forming is a main body of the can manufacturing process, thinning of the steel plate to be used has progressed. However, when the steel plate is simply thinned, a can body strength is decreased. Accordingly, for such a usage, a thin-walled can steel plate with the higher strength has been desired. In addition, an easy open end (hereinafter, referred to as EOE) used as a lid of a beverage can, a food can, or the like is provided with a tab by a rivet process, and thus formability causing no breaking by rivet forming is required.
Currently, the thin-walled can steel plate with the high strength is manufactured by a double reduce method (hereinafter, referred to as a DR method) of performing a secondary cold rolling process after an annealing process. The manufacturing process according to the DR method includes a hot rolling process, a cold rolling process, an annealing process, and a secondary cold rolling process. In the manufacturing process according to the DR method, the number of processes is more than that of the conventional manufacturing process in which the last process is the annealing process by one, and thus the cost is increased. The cost reduction is being desired even for such a can steel plate, and thus it is necessary to omit the secondary cold rolling process causing the high cost.
Accordingly, a method of manufacturing a high-strength can steel plate in processes upto an annealing process by adding a strengthening element or changing a manufacturing condition is proposed. Specifically, Patent Literature 1 discloses a method of manufacturing a steel plate with small in-plane anisotropy by performing a recrystallization annealing process after a cold rolling process. The steel plate with the small in-plane anisotropy is suitable for a can in which a process along a specific direction cannot be performed and a drawing process is performed. However, in the steel plate in which the in-plane anisotropy is not substantially a problem, it is not necessary to perform the recrystallization annealing process after the cold rolling process.
Hitherto, an as-rolled plate in which a heat treatment is not performed after a cold rolling process or a steel plate in which ductility is recovered by a heat treatment at a temperature equal to or lower than a recrystallization completion temperature has been studied. Since the strengthening element is not added to such a steel plate, an influence on corrosion resistance is small, and it can be used as a beverage can or a food can at ease. Accordingly, when it is not required that the in-plane anisotropy is small, a method of manufacturing a high-strength steel plate by performing a recovery annealing process at a temperature equal to or lower than the recrystallization completion temperature is effective. Therein, the following technique is proposed.
Patent Literature 2 discloses a technique of obtaining a steel plate with a high yield strength by performing a finish rolling process at a temperature equal to or lower than an Ar3 transformation formability at a hot rolling process, performing a cold rolling process at a rolling rate equal to or lower than 85%, and then performing a heat treatment for 10 minutes within a temperature range of 200 to 500° C.
Patent Literature 3 discloses a technique of making Rockwell hardness (HR30T) by performing an annealing process within a temperature range equal to or higher than 400° C. and equal to or lower than a recrystallization temperature after performing a cold rolling process.
Patent Literature 4 disclose a technique of obtaining a steel plate with a high elastic modulus by performing a hot rolling process at a temperature equal to or lower than an Ar3 transformation formability at a rolling reduction equal to or higher than 50% using the steel with the same composition as that of the steel disclosed in Patent Literature 3, performing a cold rolling process at a rolling reduction equal to or higher than 50%, and then an annealing process within a temperature range equal to or higher than 400° C. and equal to or lower than a recrystallization temperature. In Patent Literature 4, it is determined that a recrystallization temperature is a temperature at which a recrystallization rate is an organization of 10%.
Patent Literature 5 discloses a technique of obtaining a steel plate with a high yield strength by performing a finish rolling process in which a total rolling reduction at a temperature equal to or lower than an Ar3 transformation formability is equal to or higher than 40% at the time of a hot rolling process, performing a cold rolling process at a rolling reduction equal to or higher than 50%, and then performing an annealing process for a short time within a temperature range of 350 to 650° C.
Patent Literature 6 discloses a method of manufacturing a steel plate having full elongation equal to or higher than 5% with a tensile strength of magnitude of 550 to 600 MPa by performing an annealing process within a temperature range of (a recrystallization start temperature −200) to (a recrystallization start temperature −20)° C.
Patent Literature 7 discloses a method of manufacturing a steel plate with a tensile strength of 600 to 850 MPa by performing a hot rolling process equal to or higher than 5% and less than 50% of a total rolling reduction amount in a finish rolling process at a temperature lower than an Ar3 transformation formability, and performing an annealing process within a temperature range from 400° C. to (recrystallization temperature −20°) C.
Patent Literature 8 discloses a method of manufacturing a steel plate in which a value of (intensity of {112}<110>orientation)/(intensity of {111}<112>orientation) is equal to or more than 1.0, a tensile strength in a direction of 90° from a rolling direction in a horizontal plane is 550 to 800 MPa, and Young's modulus is equal to or higher than 230 GPa, by performing an annealing process within a temperature range of 520 to 700°.